The minister was in Scotland to announce £350million plans to replace nuclear weapons system Trident, based at Faslane on the Clyde.

Cameron has appointed one of his most senior civil servants – Cabinet Secretary Sir Jeremy Heywood – to take charge of the cross-department campaign to save the Union.

And Sir Nicholas MacPherson, the Treasury’s top civil servant, will chair a group of permanent secretaries.

They will oversee teams of top economists and civil servants, who are formulating the statistical and policy ammunition for ministers to use in questions about independence.

The documents will highlight areas of vulnerability if Scotland decides to split from the UK, while highlighting the benefits of the UK.

Government officials insist the documents will lay out the facts about the consequences of independence and will have resources to back them up – so that they can’t be dismissed by the SNP as scare-mongering.

A senior Treasury official said: “The purpose is to come up with work that is credible. The Government is not impartial but it will be academically rigorous and will not be about political point-scoring.”

However, a spokesman for Deputy First Minister Nicola Sturgeon hit back: “No matter how many reports the Tory-led, anti-independence campaign produces over the next two years, it will not change the fact that Scotland more than pays its own way.

“Official figures prove that an independent Scotland would be better off than we are in the UK to the tune of £500 per person.

“We are confident the positive case for an independent Scotland will win the day – especially when people realise that a No vote offers nothing for Scotland.

“It risks stripping away the benefits of devolution – such as free personal care for the elderly and free university education.”

The Key Questions

1 Legal basis for breaking up the UK – what will be the cost of breaking up the UK and setting up parallel systems of government in Edinburgh and London?

2 Debt and borrowing – what would be Scotland’s share of national debt and how much would Scotland have to pay for borrowing in the international markets? Every country has borrowings, but with no track record the new nation would have to pay more for loans.

3 Culture, heritage and identity – from the Queen and the Olympics to James Bond, the UK shares thousands of cultural treasures. Who gets what under independence?

4 Economic performance of Scotland – a key document asking: does Scotland do better as part of the UK or not? What would be the trade impact of a new border?

5 EU membership and international – would Scotland be member of the EU, NATO and other diplomatic organisations? Who would look after Scots abroad and how much would Scottish embassies cost?

6 Borders and immigration – if Scotland joined the EU, how would it patrol the border with England, which is not in the Schengen Agreement on free movement across EU borders?

7 Currency – what currency would be valid? If Scotland joined a sterling zone, monetary policy and interest rates would be set by the Bank of England. Would the UK agree to a shared currency?

8 Energy and oil – what would be the share of oil and gas for an independent Scotland: by geographical share or per head of population?

9 Business, innovation and infrastructure – how would Scotland finance the high speed rail line from Carlisle to Glasgow?

10 Tax and spending – how much could tax be raised in Scotland? Could Scotland spend as much without raising taxes?

11 Defence and security – how would Scotland defend itself? How would it pay for the removal of Trident and replacement jobs?

12 Financial services and banking – how would the financial sector in Scotland be regulated? How would we deal with shocks like a banking collapse?

13 Welfare – oil will run out in a generation and, by then, Scotland’s population will be older than the rest of the UK’s. How will an independent Scotland maintain public services?